Month: October 2014

I’ve been cleaning up the boxful of used Tortoises that I got at the last State Fair flea market. I’ve removed the wires from each one, cleaned up the contacts, and soldered on a header block. It’s my green frog version of the Terra Cotta Army.

These headers are .156″ spacing right angle headers, which are designed to work with Molex connectors. They work well enough on the Tortoise — whoever designed the board at Circuitron made something that almost, but not quite, works correctly with standard connectors.

I used to use the EDAC connector plugs (available from Greenway), but these are $7 or so apiece, and they only mostly work. They can be installed off by half a pin or so, which causes them to not work reliably. They also can slip off due to vibration, since the board on the Tortoise isn’t the same thickness as the plug expects.

I’m going to use the RSMC (Remote Stall Motor Controller) board, which will take a logic hi/lo signal (such as from the Arduino, or a single pole single throw toggle/pushbutton) and swap the polarity on the 12V power to the tortoise. These board have the matching connector to the headers I just soldered to all of these Tortii.

I also can wire up the rail power to the RSMC, and I’ll get the correct frog power based on the switch position. There are additional connectors that I can use for LED indicators on the fascia.

I have all the parts for the RSMC boards on my bench, except for the PC board. I’ve ordered them from Seeed Studio in China, and they’re somewhere on the way between Shenzhen and here. The total cost of the board, the components, and the connectors will be about $5 each, which certainly compares favorably to anything which uses the EDAC connector.

There’s a different edge connector available in the last few years:

This one fits a little better, but not so much that it really is much better. It does have the advantage of being easier to use on a circuit board (the Hare, of which I have one for testing, uses this connector). It’s also a little bit cheaper (about $3 each).

But nothing beats the solid connection you get from the Molex connectors. Combined with screw terminals for the other connections, I like how the RSMC is fairly easy to replace if necessary, and I don’t think they’d slip off in a Richter 8 earthquake (something my friends in California might worry about, but I don’t here in Minnesota. Thank goodness for that.)

Maybe I should get started on laying track, so I have someplace to use these sometime soon.

One thing I do besides build & operate railroads is mess around with Arduinos. These are small low-cost low-power computers that are really good for messing around with.

I’ve designed an add-on board called the cpShield, which is meant to make the Arduino into a general I/O board, mainly for use as a part of a CMRI network for model railroads. The cpShield has 16 general I/O lines, and can control a single stall motor (such as a Tortoise) or two servos.

There’s also an I2C connection for adding additional boards. There are 16 and 32 I/O line boards called the IOX16 & IOX32 that I have used.

a cpShield board with an attached Arduino Pro

The blue board is an ArduinoPro (seen from the bottom), while the green board below it is the cpShield itself.

I’ve also written code for turning this into a node on a CMRI network.

There’s a library called IOLine, which generalizes the notion of an input or output line between the Arduino pins, the IOX extender boards (which do the same thing, but with a different code interface), or internal variables.

There’s another to provide a decent interface to the IOX extender boards, which use an MCP23017 I2C chip. The library is quite unoriginally called MCP23017.

Lastly, there’s code to implement the node side of a CMRI network. You still need driver software on a central computer to run the network.

I’ve spent the last few evenings making lights blink with the Arduinos, and have recently updated the code out on Github.